Urine melatonin and citrate excretion during the elite swimmers’ training season

The objectives of the study were to evaluate the influence of a whole training season on 6-sulfatoxymelatonin (αMT6s) and citrate excretion in 12 elite swimmers. Urine samples were obtained (before bedtime and after waking up) at the beginning of the season, basic training, macrocycle I, tapering and macrocycle II stages. For αMT6s, at basic training, mainly with aerobic training, the evening concentrations were significantly lower (P < 0.01; P < 0.05) than at the beginning, tapering and macrocycle II stages. At macrocycle II stage, with the maximal training workload, the total sum (evening plus morning) was significantly higher (P < 0.05) than at the beginning, basic training and macrocycle I stages. The ratio (morning/evening) that represents the capacity to produce melatonin at night depending on the evening values at the basic training stage and the nocturnal increment at the macrocycle II stage were significantly higher (P < 0.01) than at all other stages. Citrate morning values at basic training and tapering stages were significantly lower (P < 0.01) than in the evening indicating that a metabolic recuperation took place. The total sum significantly decreased (P < 0.05) as the aerobic training progressed from the beginning to macrocycle I. The basic training ratio (morning/evening) was significantly lower compared to the beginning and macrocycle II stages, and the nocturnal increment was significantly higher (P < 0.05) compared to the beginning. Melatonin and citrate represent complementary markers that could be used to evaluate the assimilation of the training workload by noninvasive methods.